1. Field of the Invention
The present invention relates to the transport and storage of semiconductor wafers, and in particular to a system capable of storing wafer-carrying pods and/or cassettes and capable of transferring wafer-carrying pods and/or cassettes to and from a semiconductor processing tool, which system provides a high degree of flexibility, operates with a minimum amount of hardware and software control and makes efficient use of space.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
The SMIF system provides a clean environment for articles by using a small volume of particle-free gas which is controlled with respect to motion, gas flow direction and external contaminants. Further details of one proposed system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (xcexcm) to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half xcexcm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with present geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.2 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
A SMIF system includes a minimum volume, sealed pod used for storing and transporting wafers or other workpieces. Within a wafer fab, a first automated transport system is provided for transferring the SMIF pods from one processing tool bay to another (interbay delivery systems) and a second automated transport system may be provided for transferring the pods around within each particular bay (intrabay delivery systems). Tool bays are typically on the order of about 80 feet long, and consist in general of a number of processing tools for performing various wafer fabrication functions, metrology tools for monitoring or testing a wafer or wafers from within a wafer lot, and at least one stocker for storing the pods before or after processing.
Some processing tools within a tool bay are typically high throughput tools which are capable of performing their particular wafer process at a relatively higher rate than other processing tools. Similarly, as metrology tools only sample one wafer per lot, these tools also are capable of handling substrate carriers at a much higher rate than typical processing tools. Presently, a semiconductor wafer fab may cost in excess of $1.6 billion, and approximately 80% of that cost is the cost of equipment. It is therefore desirable to maximize the yield of this equipment, and substantial efforts are devoted to minimizing the time that the tools sit idle.
In order to prevent significant idle time for high throughput and metrology tools, it is known to include a local tool buffer adjacent the tool load ports of high throughput and metrology tools. In this way, pods may be stored locally adjacent such tools and quickly transferred to the tool load port without having to constantly retrieve a pod from the remotely located stocker, or depend on timely delivery therefrom. A conventional local tool buffer is shown generally at 10 adjacent a process tool 12 in FIG. 1A. As shown therein, a pod handling robot 14 is capable of transferring pod 16 between a plurality of local shelves 18 and the tool load ports 20 on the process tool. The pod handling robot 14 includes a base 21 mounted to a track 22 so as to translate along the z-axis. First and second arms 24 and 26 and a gripper 28 are attached to the base 21 and are controlled by computer to grip a pod 16 for transfer between the shelves 18 and the tool load ports 20.
Conventional local buffers, such as that shown in FIG. 1A, have several shortcomings. First, it is the nature of the robot used therein that it can only reach one carrier space to its left or right. Thus, the storage spaces available to such a robot are limited to being directly adjacent the robot. A second significant shortcoming of conventional local buffers is that they utilize three-dimensional transport of the pods. That is, the pods are transported outside of the X-Z plane in which they are stored. The footprint of such conventional buffers must be large enough to accommodate this three-dimensional transport.
A still further shortcoming to conventional local buffers relates to the storage density of such systems. Storage density refers to the ratio of storage space available to the overall footprint required by the local buffer. FIG. 1B is a graphical representation of the storage density of the local buffer shown in FIG. 1A (each box represents a space capable of being occupied by a single wafer-carrying pod), with the outline of the robot provided thereon. As shown, storage spaces are available in the lower left and right positions 1 and 2 of the buffer. As the track 22 must be off-set from the robot in order to allow pods to be passed in front of the robot (i.e., between the robot and the buffer wall), the lower middle space is utilized for vertical pod travel and is unavailable for pod storage. Similarly, the spaces to the left and right of the robot base (in the top center) are inaccessible due to the position of the stored pod and track 22. Thus the resulting storage density for a two-deep local buffer is 2 to 6, or 33%.
A mechanism similar to that shown in FIG. 1A may be used as a stocker for pod storage. Such conventional stockers may additionally include a second bank of storage spaces juxtaposed to the first bank. The storage density of this system is graphically represented in FIG. 1C. As shown, the robot may be configured to translate in the direction of arrow Axe2x80x94A. By adding the additional bank, the storage density improves to 4 to 9, or about 45%. However, this is still a relatively low ratio, and it comes at the expense of a large footprint.
It is therefore an advantage of the present invention to provide a process tool storage, delivery and retrieval system for supplying pods to semiconductor process and metrology tools.
It is another advantage of the present invention to provide two-dimensional transport of a wafer carrier, wherein a carrier is transported in the same plane in which it is stored
It is a further advantage of the present invention to provide a storage space for wafer carriers having a maximum storage density within a minimum incremental footprint relative to the process tool""s original footprint without the buffer.
It is a still further advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system having a small overall footprint.
It is another advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system which may be easily scaled to different sizes.
It is a further advantage of the present invention to provide a highly reliable tool integrated pod storage, delivery and retrieval system.
It is another advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system capable of minimizing the creation of particulates in the cleanroom.
It is a further advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system capable of minimizing tool idle time.
It is a further still advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system of highly flexible design, easily adapted to variously configured process tools and pod delivery systems.
It is another advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system having a simple design and requiring relatively little maintenance.
It is a further advantage of the present invention to provide a tool integrated pod storage, delivery and retrieval system which may coexist safely with human operators working near the process tools.
These and other advantages are accomplished by the present invention, which in preferred embodiments relates to a pod storage, delivery and retrieval system capable of providing an improved local tool buffer for various semiconductor process tools or an improved stocker for storing pods in a semiconductor tool bay. A basic embodiment of the invention comprises a structure having a rear wall to which is affixed a plurality of shelves capable of supporting one or more wafer-carrying pods. The structure further includes a pair of vertical rails lying in a plane spaced from and substantially parallel to the shelf-supporting wall. A horizontal rail extends between and is translationally mounted to the vertical rails, which horizontal rail supports a gripper capable of movement along the horizontal rail. The movement of the horizontal rail along the vertical rails, and the movement of the gripper along the horizontal rail, allows the gripper to be positioned at any location within an X-Z plane including the storage shelves.
In one embodiment of the invention, the above-described storage, delivery and retrieval system may be mounted to the front surface of a process tool. Process tools conventionally include tool load ports protruding from the front of the tool into the tool bay. The storage, delivery and retrieval system according to the present invention preferably fits over the tool load port so as not to increase the depth of the tool (i.e., the distance of the tool away from the tool bay wall) beyond that occupied by the tool load port.
In a preferred embodiment, the shelves are provided within the storage, delivery and retrieval system in a plurality of rows and columns defining spaces in which the gripper may translate vertically and horizontally. The shelves may be provided in various configurations, including being one, two, or more deep in a direction perpendicular to the X-Z plane, and may also have one, two, or more shelves directly adjacent to each other in the X-Z plane. It is a feature of the present invention that the gripper, when not gripping a pod, may translate horizontally through shelves having a pod thereon. The movement of the gripper along the horizontal rail, and the movement of the horizontal rail along the vertical rails, may be controlled so that the system may transfer pods between the storage shelves and the tool load port of the process tool.
It is a feature of the present invention that the above-described transport system is a two-dimensional transport system. That is, all transport of the pods between the ports and the storage shelves occurs without the pods ever leaving the X-Z plane of the ports and the shelves. This feature contributes to the overall small footprint of the system. Additionally, the gripper moves around in the same plane as the pods, and the rails have a small profile and operate directly adjacent the storage shelves. These features further contribute to the small footprint of the system.
The present storage, delivery and retrieval system may be provided in various orientations with respect to the process tool it is serving. In one embodiment, the system may be mounted on the front surface of a process tool, around the tool load port, and extending approximately the depth of one pod into the tool bay. In a further embodiment of the invention, the process tool and storage, delivery and retrieval system may be moved back such that the front of the storage, delivery and retrieval system adjacent the tool bay is flush with the tool bay wall. In this embodiment, various configurations of shelves may extend from the storage, delivery and retrieval system into the tool bay to receive a pod from the standard intrabay pod delivery mechanisms.
In a further embodiment of the present invention, the storage, delivery and retrieval system may be mounted to the side of a process tool, entirely within the space behind the process tool bay wall and in between adjacent process tools. In this embodiment, the storage, delivery and retrieval system may include various configurations of shelves extending out of the side of the system and into the tool bay for receiving a pod from the intrabay pod delivery systems. Alternatively, the storage, delivery and retrieval system may itself extend partially into the tool bay to receive a pod from the delivery system.
In a further embodiment of the present invention, two or more storage, delivery and retrieval systems may service a single processing tool. In this embodiment, the systems may be oriented side-by-side at the front or side of a processing tool. Alternatively, the systems may be provided back-to-back at the front or side of the process tool. Various configurations of conveyors and/or telescoping shelves may be provided for transferring pods between the adjacent systems of the multiple storage, delivery and retrieval systems. It is also contemplated that conveyors may be provided for linking storage, delivery and retrieval systems mounted on separate process tools. In a further embodiment of the present invention, a single storage, delivery and retrieval system may be sized to serve and link more than one process tool.
In a still further embodiment, the present invention may comprise a standalone stocker for storing a plurality of pods. As in the embodiments of the invention comprising a local tool buffer, owing in part to the ability of the present invention to transport pods in the same plane in which they are stored, the ability of the gripper to travel around in the same plane as the pods, and the small profile of the transport rails, the stocker according to the present invention may operate in an extremely small footprint.